Java example source code file (Launcher.c)

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Java - Java tags/keywords

dir, java_launcher_launch0, jnicall, jnienv, jniexport, null, o_rdonly, stderr_fileno, stdin_fileno, stdout_fileno, throwexception

The Launcher.c Java example source code

/*
 *
 *
 * A simple launcher to launch a program as if it was launched by inetd.
 */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <ctype.h>

#include "jni.h"

#include "Launcher.h"

/*
 * Throws the exception of the given class name and detail message
 */
static void ThrowException(JNIEnv *env, const char *name, const char *msg) {
    jclass cls = (*env)->FindClass(env, name);
    if (cls != NULL) {
        (*env)->ThrowNew(env, cls, msg);
    }
}

/*
 * Convert a jstring to an ISO 8859_1 encoded C string
 */
static char* getString8859_1Chars(JNIEnv *env, jstring jstr) {
    int i;
    char *result;
    jint len = (*env)->GetStringLength(env, jstr);
    const jchar *str = (*env)->GetStringCritical(env, jstr, 0);
    if (str == 0) {
        return NULL;
    }

    result = (char*)malloc(len+1);
    if (result == 0) {
        (*env)->ReleaseStringCritical(env, jstr, str);
        ThrowException(env, "java/lang/OutOfMemoryError", NULL);
        return NULL;
    }

    for (i=0; i<len; i++) {
        jchar unicode = str[i];
        if (unicode <= 0x00ff)
            result[i] = unicode;
        else
            result[i] = '?';
    }

    result[len] = 0;
    (*env)->ReleaseStringCritical(env, jstr, str);
    return result;
}


/*
 * Class:     Launcher
 * Method:    launch0
 * Signature: ([Ljava/lang/String;I)V
 */
JNIEXPORT void JNICALL Java_Launcher_launch0
  (JNIEnv *env, jclass cls, jobjectArray cmdarray, jint serviceFd)
{
    pid_t pid;
    DIR* dp;
    struct dirent* dirp;
    int thisFd;
    char** cmdv;
    int i, cmdlen;

    /*
     * Argument 0 of the command array is the program name.
     * Here we just extract the program name and any arguments into
     * a command array suitable for use with execvp.
     */
    cmdlen = (*env)->GetArrayLength(env, cmdarray);
    if (cmdlen == 0) {
        ThrowException(env, "java/lang/IllegalArgumentException",
            "command array must at least include the program name");
        return;
    }
    cmdv = (char **)malloc((cmdlen + 1) * sizeof(char *));
    if (cmdv == NULL) {
        ThrowException(env, "java/lang/OutOfMemoryError", NULL);
        return;
    }

    for (i=0; i<cmdlen; i++) {
        jstring str = (*env)->GetObjectArrayElement(env, cmdarray, i);
        cmdv[i] = (char *) getString8859_1Chars(env, str);
        if (cmdv[i] == NULL) {
            return;
        }
    }

    /*
     * Command array must have NULL as the last entry
     */
    cmdv[cmdlen] = NULL;

    /*
     * Launch the program. As this isn't a complete inetd or Runtime.exec
     * implementation we don't have a reaper to pick up child exit status.
     */
#ifdef __solaris__
    pid = fork1();
#else
    pid = fork();
#endif
    if (pid != 0) {
        if (pid < 0) {
            ThrowException(env, "java/io/IOException", "fork failed");
        }
        return;
    }

    /*
     * We need to close all file descriptors except for serviceFd. To
     * get the list of open file descriptos we read through /proc/self/fd
     * but to open this requires a file descriptor. We could use a specific
     * file descriptor and fdopendir but Linux doesn't seem to support
     * fdopendir. Instead we use opendir and make an assumption on the
     * file descriptor that is used (by opening & closing a file).
     */
    thisFd = open("/dev/null", O_RDONLY);
    if (thisFd < 0) {
        _exit(-1);
    }
    close(thisFd);

    if ((dp = opendir("/proc/self/fd")) == NULL) {
        _exit(-1);
    }

    while ((dirp = readdir(dp)) != NULL) {
        if (isdigit(dirp->d_name[0])) {
            int fd = strtol(dirp->d_name, NULL, 10);
            if (fd != serviceFd && fd != thisFd) {
                close(fd);
            }
        }
    }
    closedir(dp);

    /*
     * At this point all file descriptors are closed except for
     * serviceFd. We not dup 0,1,2 to this file descriptor and
     * close serviceFd. This should leave us with only 0,1,2
     * open and all connected to the same socket.
     */
    dup2(serviceFd, STDIN_FILENO);
    dup2(serviceFd, STDOUT_FILENO);
    dup2(serviceFd, STDERR_FILENO);
    close(serviceFd);

    execvp(cmdv[0], cmdv);
    _exit(-1);
}